This application claims priority under 35 U.S.C. Sec. 119 to a patent application No. 2001-388471 filed in Japan on Dec. 20, 2001, the entire content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method for setting a helical compression spring and an apparatus for setting the same, and more particularly to the method and apparatus for setting a formed helical compression spring by placing the formed helical compression spring between a pair of compression plates, and pressurizing the formed helical compression spring, to produce a helical compression spring specially for use in a vehicle suspension system.
2. Description of the Related Arts
Various helical compression springs have been known heretofore. Among them, there is a helical compression spring which is designed to provide a coil axis that does not coincide with a direction of reaction force of the spring. For example, there is a helical compression springs for use in the vehicle suspension system, which has a reaction force axis inclined at a predetermined angle so as to lie on a predetermined position of an upper end coil or a lower end coil. When producing that spring, it is required to obtain a predetermined reaction force axis.
As for a conventional process for producing the helical spring, there are known a cold working process for forming a steel coil wire at a room temperature, and a hot working process for heating the coil wire to form it. The former method is disclosed in Japanese Patent Laid-open Publication No. 2000-345238, for example, and the latter method is disclosed in Japanese Patent Laid-open Publication No. H10-237546, for example. Neither Publications describe adjusting the reaction force axis.
One of the inventors of the present application filed a U.S. patent application Ser. No. 09/976,158 on Oct. 15, 2001, which was published on Apr. 25, 2002 as Publication No. US-2002-0046587-A1, in which an invention of a method and apparatus for producing a compression spring was proposed. According to this method, a compression spring having a predetermined reaction force axis can be produced by the cold working process. In the case where the compression spring is produced by the hot working process, however, it is difficult to form the spring in a desired coiling shape, so that it is not easy to adjust the reaction force axis. Furthermore, after the compression spring is produced, and thereafter a reaction force axis of the finished product is measured, provided that the conditions for hot working are modified so as to clear an error between a target reaction force axis and the reaction force axis of the finished product, it will take a quite long time to produce the spring due to unnecessary steps required for doing so. In addition, it will be required to produce a large number of springs at once in the same conditions, and it will be almost impossible to modify them on a product by product basis.
In the above-described Japanese Patent Laid-open Publication No. 2000-345238, there is disclosed a hot setting process for applying a predetermined load on a coil spring in a higher temperature condition than a room temperature, to compress and hold it. It was noticed by the present inventors that the reaction force axis could be adjusted, with a desired spring property maintained, by controlling the hot setting process as described later. According to this process, the reaction force axis could be adjusted, by means of hot setting process (or, warm setting process), after the compression spring was formed by the hot working process as described before, while it had been difficult to adjust the reaction force axis. However, the reaction force axis could not be adjusted, by means of a conventional hot setting process (i.e., prior hot setting process), which would cause a large deformation to result in a large dispersion of the reaction force axis.
Accordingly, it is an object of the present invention to provide a method for setting a helical compression spring, by placing a formed helical compression spring between a pair of compression plates, and pressurizing the formed helical compression spring, so that the compression spring could be adjusted to provide a desired reaction force axis.
It is another object of the present invention to provide an apparatus for setting a formed helical compression spring to provide a desired reaction force axis.
In accomplishing the above and other objects, a method for setting a helical compression spring is performed by placing the formed helical compression spring between a pair of compression plates, tilting at least one of the compression plates by a predetermined angle to an end plane of the spring, and actuating at least one of the compression plates to pressurize the spring.
The method may include the steps of (1) a measuring step for measuring parameters to detect a reaction force axis of the formed helical compression spring, (2) a determination step for comparing a target reaction force axis of the spring with the reaction force axis detected on the basis of measured parameters to provide an error between the target reaction force axis and the detected reaction force axis, (3) a tilt angle providing step for providing a tilt angle of at least one of the compression plates tilted to an end plane of the spring, in at least one direction on a plane including a coil axis of the spring, on the basis of the error provided at the determination step, and (4) a pressure step for actuating at least one of the compression plates to pressurize the spring, with at least one of the compression plates tilted to the end plane of the spring by the tilt angle provided at the tilt angle providing step.
In the method, the tilt angle providing step may be adapted to provide a first tilt angle of at least one of the compression plates tilted to an end plane of the spring, in one direction on one plane including the coil axis of the spring, and a second tilt angle of the one of the compression plates tilted to the end plane of the spring, in the other direction on a plane perpendicular to the one plane, on the basis of the error provided at the determination step. And, the pressure step may be adapted to actuate at least one of the compression plates to pressurize the spring, with at least one of the compression plates tilted to the end plane of the spring by the first and second tilt angles provided at the tilt angle providing step.
In the method as described above, it is preferable to pressurize the formed spring between the compression plates, in such a condition that the formed spring is heated within a predetermined temperature range.
An apparatus for setting a formed helical compression spring includes a measuring device for measuring parameters to determine a reaction force axis of the formed helical compression spring, a determination device for comparing a target reaction force axis of the spring with the reaction force axis determined by the measured parameters to provide an error between the target reaction force axis and the detected reaction force axis, a tilt angle providing device for providing a tilt angle of at least one of the compression plates tilted to an end plane of the spring, in at least one direction on a plane including a coil axis of the spring, on the basis of the error provided at the determination device, and a pressure device for actuating at least one of the compression plates to pressurize the spring, with at least one of the compression plates tilted to the end plane of the spring by the tilt angle provided at the tilt angle providing device.
In the apparatus, the tilt angle providing device may be adapted to provide a first tilt angle of at least one of the compression plates tilted to an end plane of the spring, in one direction on one plane including the coil axis of the spring, and a second tilt angle of the one of the compression plates tilted to the end plane of the spring, in the other direction on a plane perpendicular to the one plane, on the basis of the error provided at the determination device. And, the pressure device may be adapted to actuate at least one of the compression plates to pressurize the spring, with at least one of the compression plates tilted to the end plane of the spring by the first and second tilt angles provided at the tilt angle providing device.
In the apparatus as described above, it is preferable to pressurize the formed spring between the compression plates, in such a condition that the formed spring is heated within a predetermined temperature range.